Commercial nonwoven fabrics typically comprise synthetic polymers formed into fibers. These fabrics are typically produced with solid fibers that have a high inherent overall density, typically 0.9 g/cm3 to 1.4 g/cm3. The overall weight or basis weight of the fabric is often dictated by a desired opacity, mechanical properties, softness/cushiness, or a specific fluid interaction of the fabric to promote an acceptable thickness or caliper, strength and protection perception. Often, these properties are needed in combination to achieve a particular function or a desired level of performance.
Functionality of nonwoven fabrics is important for many applications. For many nonwoven applications, its function is to provide a desired feel to a product by making it softer or feel more natural. For other nonwoven applications, its function affects the direct performance of the product by making it absorbent or capable of acquiring or distributing fluid. In either case, the function of the nonwoven is often related to the caliper or thickness. For instance, nonwoven fabrics are useful for fluid management applications desiring optimal fluid acquisition and distribution capabilities. Such applications include use in disposable absorbent articles for wetness protection and cleaning applications for fluid and particulate clean-up. In either case nonwoven fabrics are desired for use as a fluid management layer having capacity to acquire and distribute fluid.
The effectiveness of the nonwoven fabric in performing this function is largely dependent upon the thickness or caliper and corresponding void volume of the nonwoven fabric as well as the properties of the fibers used to form it. For many applications caliper also needs to be limited so that bulkiness of the resulting product is minimized. For instance, a disposable absorbent article typically includes a nonwoven topsheet a backsheet and an absorbent core therebetween. In order to control leakage and rewet due to gushing, a fluid acquisition layer that typically comprises at least one nonwoven layer is disposed between the topsheet and the absorbent core. The acquisition layer has capacity to take in fluid and transport it to the absorbent core. The effectiveness of the acquisition layer in performing this function is largely dependent upon the thickness of the layer and the properties of the fibers used to form it. However, thickness leads to bulkiness which is undesirable to the consumer. Therefore, the thickness or caliper of a nonwoven is selected based on a balance of maximum thickness for functionality and minimal thickness for comfort.
In addition, the caliper of a nonwoven fabric is often difficult to maintain due to compressive forces induced during material handling, storage and in some applications, ordinary use. Therefore, for most applications it is desirable for a nonwoven to exhibit a robust caliper that is sustainable through converting, packaging and end use. What's more, high caliper nonwoven fabrics take up more space on rolls during storage. Thus, it is also desirable have a process for increasing the caliper of a nonwoven fabric preferably not until the point in time when it enters the process used in manufacturing a particular end product so that more material can be stored on a roll before it is converted to a final product.